Conventionally, as refrigerants for cold storage chambers, car air-conditioners, room air-conditioners, industrial refrigerating machines and the like, 1,1,1,2-tetrafluoroethane (R134a), R410A that is a mixed refrigerant of 1/1 (mass ratio) of difluoromethane (R32) and pentafluoroethane (R125), which are hydrofluorocarbons (HFC), and the like have been widely used.
As refrigerating machine oils used together with the above-described HFC refrigerants, there are those into which various additives are blended so as to improve a lubricating property.
It is to be noted that, in a general field of lubricant oils, as antiwear additives for improving a lubricating property, oiliness agents such as alcohols, esters, and long-chain fatty acids, antiwear agents such as phosphates and metal dithiophosphates, and extreme pressure agents such as organic sulfur compounds and organic halogen compounds are known. However, in the case of refrigerating machine oils, only additives which do not precipitate when coexisting with refrigerants and do not have a negative effect on stability can be used, and thus, alcohol or ester oiliness agents, and, among phosphates, triphenyl phosphate and tricresyl phosphate are used.
Moreover, Patent Literature 1 discloses a refrigerating machine lubricant oil to which a phosphorous additive and a specific epoxy compound are added together, Patent Literature 2 discloses a compressor lubricant oil for a HFC refrigerant, to which triphenyl phosphate and tri(alkylphenyl) phosphate are added together, and Patent Literature 3 discloses a refrigerating machine oil for a HFC refrigerant, to which tricresyl phosphate, and an epoxy compound consisting of glycidyl ether, or carbodiimide are added, respectively.